Project Summary/Abstract Chronic disease and declining physical function are significant problems facing the growing population of older breast cancer survivors. Physical activity can reduce the risk of developing chronic disease and prevent functional decline in older breast cancer survivors; however, only 25% of older cancer survivors meet national guidelines for physical activity. Evidence suggests that physical activity can improve executive and other cognitive functions in cancer survivors; however, executive functioning may also affect physical activity. Problems with executive function may interfere with self-regulatory abilities necessary to initiate and sustain physical activity habits. Although some support for this hypothesis has been found in older adults without cancer, researchers have not extended this work to older breast cancer survivors, a population at greater risk of cognitive decline compared to age-matched controls. If lowered executive function is associated with lower physical activity at follow-up, findings would support future physical activity interventions which include cognitive training or compensation strategies for lowered executive function. Additionally, several risk factors for accelerated cognitive decline in older breast cancer survivors have been proposed. These risk factors include older age, more advanced cancer stage, multiple comorbid medical conditions, and the presence of at least one ?4 allele in the APOE genotype. These risk factors may also impact the relationship between executive function and physical activity. The proposed study is a secondary analysis of a prospective study of older breast cancer survivors, the Thinking and Living with Cancer (TLC) cohort study (R01CA129769). The TLC study is the only large prospective examination of objective cognitive function in older breast cancer survivors before systemic cancer therapy and 1 and 2 years later as well as contemporaneously assessed controls. Measures at each time point include neuropsychological tests of executive function and self-reported physical activity. Objective physical activity data are also available for a subsample of participants. The primary aim of the proposed project is to examine two hypotheses regarding the association between executive function change and physical activity in 346 older (60+ years of age) breast cancer survivors during the two years post-diagnosis and 356 matched controls. The primary hypothesis is that executive function decline from baseline to year 1 will predict lower physical activity at year 2. The secondary hypothesis is that lower physical activity at year 1 will predict decline in executive function from year 1 to year 2. This study also aims to explore whether the relationship between executive function change and physical activity differs for breast cancer survivors with selected risk factors for accelerated cognitive decline. Results will inform future physical activity interventions in order to slow functional decline and reduce the burden of chronic disease.